The invention relates to a process for the modification of (co)polymers by reacting them with organic peroxides in the presence of a co-agent, and to shaped products composed of these modified (co)polymers.
It is generally known that modifying appropriate (co)polymers with organic peroxides in the presence of a co-agent may result in improved physical properties of the (co)polymers. Conventional co-agents are polyfunctional reactive additives promoting the formation of networks. They react with polymer radicals very rapidly, prevent steric effects, and minimize objectionable side reactions such as radical-induced polymer degradation.
Monomeric co-agents which are frequently used are allyl-containing compounds, such as triallyl cyanurate (TAC), and (meth)acrylates, such as ethylene glycol dimethacrylate. There are, however, several drawbacks to these co-agents. First of all, many of the above-mentioned compounds have a disagreeable odour and are volatile and thus cause problems when processed at relatively high temperatures. Secondly, the elongation at rupture of cross-linked (co)polymers decreases as the amount of a monomeric co-agent processed with a (co)polymer is increased. This renders it virtually impossible to prepare (co)polymers combining a low compression set and a high elongation at rupture by employing these known monomeric co-agents. Low compression set and a high elongation rupture are particularly desirable for (co)polymers used in seals and sections in, for instance, the automotive industry. Also, the known co-agents are generally incapable of preventing unacceptable amounts of radical-induced polymer degradation.
In addition to said monomeric co-agents, some polymeric co-agents are also known. Commercially available polymeric co-agents are typically polybutadiene formulations. When combined with organic peroxides these polybutadiene formulations have the disadvantage that they have to be added in relatively large amounts in order to obtain the desired degree of cross-linking.
Chemtech (August 1986) pp. 500-504 discloses polymers of 1,3- and 1,4-diisopropenylbenzene and their preparative process. In this article it is also mentioned that mixtures of the monomeric compounds 1,3- and 1,4-diisopropenylbenzene, when copolymerized with styrene, were found to be less efficient cross-linking agents than conventional cross-linking agents.
The invention overcomes the above-indicated drawbacks associated with the use of the co-agents, and to this end provides a process in which particular co-agents are employed for the modification of (co)polymers in the presence of an organic peroxide.